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SOIL-GAS RADON INTERCOMPARISONS
Martin
Neznal1,
Matej
Neznal1, Milan Matolin2
1RADON v.o.s.,
Novakovych
6, 180 00 Praha
8, Czech Republic, e-mail: [email protected]
2Charles University in Prague, Faculty of Science, Albertov 6, 128 43 Praha 2,
Czech Republic,
e-mail: [email protected]
SOIL-GAS RADON INTERCOMPARISON MEASUREMENTS –
HISTORY
SYSTEM OF SOIL-GAS RADON DATA STANDARDIZATION IN THE CZECH REPUBLIC
SOIL-GAS RADON INTERCOMPARISON MEASUREMENT, CZECH REPUBLIC, 2010 (RIM 2010)
SOIL-GAS RADON INTERCOMPARISON MEASUREMENTS –
HISTORY (1991 –
2002)
Badgastein, Austria, 1991CLIFF, K. D. – HOLUB, R. F. – KNUTSON, E. O. – LETTNER, H. – SOLOMON, S. B. (1994): International intercomparison of measurements of radon and radon decay products, Badgastein, Austria, September, 29 - 30, 1991, published by National Radiological Protection Board, Chilton, Didcot, Oxon.
New York, U.S.A., 1995 HUTTER, A. R. – KNUTSON, E. O. (1998): An International intercomparison of soil gas radon and radon exhalation measurements, Health Physics, Vol. 74, pp. 108-114.
Prague, Czech Republic, 1996 NEZNAL, M. – NEZNAL, M. – SMARDA, J. (1997): Intercomparison measurement of soil-gas radon concentration, Radiation Protection Dosimetry, Vol. 72, pp. 139-144.
Buk (near Pribram), Czech Republic, 2002 NEZNAL, M. – NEZNAL, M. (2004): International intercomparison measurement of soil-gas radon concentration, of radon exhalation rate from building materials and of radon exhalation rate from the ground, in Radon investigations in the Czech Republic, edited by I. Barnet, M. Neznal and P. Pacherova (Czech Geological Survey and RADON v.o.s, Prague), Vol. 10, pp. 12-22.
Badgastein, Austria, 1991Site for the measurement of soil-gas radon concentration was sloping, with an inclination of 35 –
40 degrees, partly meadow,
partly under trees. There was a thin soil layer at the site, with the underlying rock having high permeability and porosity.
Soil-gas radon concentrations were reported by 7 participants.
Large spectrum of methods: soil-gas sampling using a small- diameter hollow steel probe and Lucas cells x soil-gas radon
concentration calculated from measured radium concentration (assuming emanation coefficient 0.3 –
0.4 and porosity 0.4).
Different sampling depths: 15 –
80 cm.
Very large variability of soil-gas radon concentration at the test site.
⇒ no way to compare the results
Badgastein, Austria, 1991
New York, U.S.A., 1995First step: primary verification of Lucas cells in the Environmental Measurements Laboratory
New York, U.S.A., 1995
New Jersey, Cheesquake Parc, 16-06-1995
New York, U.S.A., 1995The sampling area was an open field (meadow), bordered by woods on two sides and a paved parking area and a paved road on the other two sides. The site had a 2-m deep soil layer underlain by a 17-m layer of marl and sand, which was situated on top of metamorphic bedrock. The soil had alternating layers that
were clay-rich and sand-rich.
Soil-gas radon concentrations were reported by 11 participants.
Different sampling depths: 0.4 –
0.5 m; 0.6 –
0.75 m; 0.9 –
1.0 m.
Variability of results described by the SD/mean ratio:
0.4 –
0.5 m
1.20
0.6 –
0.75 m
0.36
0.9 –
1.0 m 0.27
New York, U.S.A., 1995
Prague, Czech Republic, 1996
Zdiby, northern outskirts of Prague, 16-09-1996
Prague, Czech Republic, 1996Test site:open field (meadow), agriculturally cultivated (time after the harvest)
bedrock formed by Cretaceous marlites, bedrock weathering extensive and almost regular (clays, locally clayey sands)
clays covered by Tertiary sandy gravel fluvial and lacustrine sediments
the uppermost layer: Quarternary aeolic sediments –
loess (3 –
4 m) covered by organic rich clayey loam (0.5 m)
Permeability of soil:
medium to lowIn situ measurements at the depth of 1 m: 0.1 x 10-13
–
5.5 x 10-13
m2
Content of natural radionuclides in loess samples:238U: 72 –
91 Bq/kg
226Ra: 50 –
62 Bq/kg232Th: 41 –
51 Bq/kg
40K: 564 –
624 Bq/kg
Soil-gas radon concentrations reported by 10 participants
Prague, Czech Republic, 1996Results
Variability with depth described by the SD/mean ratio:
0.6 -
0.7 m
0.25
0.75 –
0.8 m
0.21
0.9 –
1.0 m 0.25
Prague, Czech Republic, 1996Results –
spatial variability
Spatial variability described by the SD/mean ratio:
points 1, 5, 9, 10, 13, 14, 15
0.21
points 2, 3, 4, 6, 7, 8, 11, 12, 16
0.20
Buk (near Pribram), Czech Republic, 2002
Buk, 20-09-2002
Buk (near Pribram), Czech Republic, 2002
Test site:Geological basement is formed by a medium grained biotitic and amphibol-biotitic granodiorite (Milin type) of the Central Bohemian pluton of Paleozoic age. The eluvial granitic material forms the cover.
Expected values of soil gas radon concentration are relatively high, soil is highly permeable at the test site. A meadow is on the surface. (Matolin, M. Radon Reference Sites in the Czech Republic. In: Barnet, I.; Neznal, M., eds. Radon Investigations in CR. Vol. 9. Praha: Czech Geological Survey and Radon corp.; 2002: 26-29)
Recommended sampling depth: 0.8 m
Soil-gas radon concentrations were
reported by 8 participants.
Buk (near Pribram), Czech Republic, 2002
Results:
Buk (near Pribram), Czech Republic, 2002
Results –
variability with depth and time:
Buk (near Pribram), Czech Republic, 2002
Results –
spatial variability:
Total variability described by the SD/mean ratio: 0.33
Some problems with primary calibration cannot be excluded.
⇒ lower values in the surroundings of point No. 4
EXPERIENCES (INTERCOMPARISONS 1991 –
2002):
From the metrological point of view, there are many serious problems connected with organizing any field intercomparison measurement of soil-gas radon concentration and similar parameters. The natural geological environment is almost never homogeneous.Measured parameters may vary, often very greatly, over a small distance.
Comparison based of single values is almost worthless. Every participant should report a set of measured values.
All participants should measure the soil-gas radon concentration at the same depth below the ground surface.
Geological conditions in a depth of soil-gas sampling as well as conditions on the soil surface should be as homogeneous as possible at the test site.
EXPERIENCES (INTERCOMPARISONS 1991 –
2002):
„Classical“ field intercomparison measurements are not intended to be used as an intercalibration of methods and instruments. Measured values are not reported against a standard or reference measurement.Participants results are compared to each other, in order to obtain an indication of the collective precision of various measurements.
Incidence of outsider values may strongly influnce the results of the intercomparison measurement.
Differences connected with primary calibration are usually lower than 10 percent.
Differences on the level of about 20% seem to be a realistic target for intercomparison measurements of soil-gas radon concentration. If the variability is much larger than 20%, problems with soil-gas sampling and/or with primary calibration are indicated.
EXPERIENCES (INTERCOMPARISONS 1991 –
2002):
Frequent systematic failures are connected with soil-gas sampling.If the sampling system is not sealed perfectly, the soil-gas samples are „contaminated“ by the atmospheric air. The real soil-gas radon concentrations are then underestimated. For testing the applicability of sampling methods, it is useful to choose a test site characterized by medium, or low permeability of soil.
Preliminary measurements should be limited at a chosen test site to avoid a destruction of the upper soil layers (the upper soil layers should not remind of a Swiss cheese). This is very important if radon exhalation from the ground surface is measured at the same test site.
SYSTEM OF SOIL-GAS RADON DATA STANDARDIZATION IN THE CZECH REPUBLICabout 100 institutions
(mostly private firms) dealing with the determination
of radon index of building sites
(= measurement of soil-gas radon concentration
and classification of permeability of soil)
each subject
has to pass the training course „Determination of radon index of building sites“
has to pass the intercomparison measurement of soil-gas radon concentration at three field radon reference sites
administrator: Charles University in Prague, Faculty of Science; 3 different levels of soil-gas radon concentration
has to verify regularly all measurement devices for the determination of soil-gas radon concentration in radon chamber
has to get the authorization from the State Office for Nuclear Safety
The procedure was used in the last soil-gas radon international intercomparison exercise (Czech Republic, 2010).
This approach represents a step from a „classical“
field intercomparison
measurement to a standardization.
SYSTEM OF RADON DATA STANDARDIZATION IN THE CZECH REPUBLICNational radon chamber:
•
Verification of instrument, its
function,
(Located
in Příbram) sensibility
and calibration,•
Verification of
data
processing.
National radon chamber was levelled with PTB Braunschweig, GER
Radon reference sites:
•
Test of soil gas
sampling,(Located in the central
•
Transfer of soil gas
sample
Bohemia) and its timing,•
Test of
the
radon instrument and its
function,•
Elimination of thoron,
•
Stability of field operation,•
Test
of correct data processing.
Charles University in Prague
Charles University in Prague
CHARACTERISTICS OF RADON REFERENCE SITES, CZECH REPUBLIC
Radon reference sitesNumber of stations at each site: 15Grid of stations: 5x5 mDistance of the 3 reference sites: 12 km
+meadow3.6LSgranodioriteH155Buk+meadow2.3LS,CSorthogneiss(L),(M),H52Bohostice
+meadow2.0SLorthogneissL,(M),H32Cetyne
Access for cars
TerrainU (ppm)
SoilBasementrock
Permeab. of soil
cA222Rn
(kBq/m3)Reference
site
+meadow3.6LSgranodioriteH155Buk+meadow2.3LS,CSorthogneiss(L),(M),H52Bohostice
+meadow2.0SLorthogneissL,(M),H32Cetyne
Access for cars
TerrainU (ppm)
SoilBasementrock
Permeab. of soil
cA222Rn
(kBq/m3)Reference
site
Charles University in Prague
TEMPORAL VARIATIONS OF RADON IN SOIL GAS AT REFERENCE SITES 2000 -
2009
Median
0
20
40
60
80
100
120
140
160
180
200
220
27.09
.2000
10.11
.2000
07.11
.2002
29.04
.2003
23.10
.2003
27.04
.2004
28.04
.2004
29.04
.2004
30.04
.2004
03.05
.2004
04.05
.2004
29.06
.2004
30.06
.2004
01.07
.2004
30.09
.2004
19.07
.2005
11.10
.2005
12.09
.2006
27.06
.2007
26.09
.2007
25.06
.2008
01.10
.2008
12.05
.2009
30.09
.2009
01.10
.2009
Date of measurement
c A (k
Bq/
m3 )
BukBohosticeCetyně
Temporal variations of radon activity concentration in soil gas at reference sitesCetyne, Bohostice
and Buk, the Czech Republic.
0 5 10 15 20 25 30 35 40 45
cA (kBq/m3)Cetynì
0
25
50
75
100
125
150
175
200
225
Buk
c A (k
Bq/
m3 )
r = 0,86
TESTS AT RADON REFERENCE SITES
Computer programmeTestMOAR
Test 1Comparison with the group
Test 2Comparison withthe group
Charles University in Prague
TESTS AT RADON REFERENCE SITES
Test 3Comparison
with
the
radon database
Testing
criterion
R1/R2of
an
ideal
value
equal
to one
and acceptabledeviations +/-
30 %;
R1/R2 <0.7 –
1.3>
Charles University in Prague
Ideal valueis 1.000
SOIL-GAS RADON INTERCOMPARISON MEASUREMENT, CZECH REPUBLIC, 2010
(RIM 2010)
Buk, Cetyne, Bohostice, 20 and 21-09-2010
RIM 2010
Final report not yet published.
All participants have already obtained the above mentioned protocol from the administrator of Czech reference sites (Charles University in Prague).
Test 2
–
linear regression y = a + bx ( blue) between radon activity concentration cA
reported by the organization (y) and medians of cA
(x) of all organizations in the group. Ideal regression line (a = 0, b = 1)
is marked red.
c
Aof
the organization [kBq/m3]
Median of cA
of all organizations in the group [kBq/m3]
Test No. 2: Linear regression y = a + bx
of radon activity concentration reported by an organization (y) at a single station and median (x) of radon activity concentration of the group of organizations at the same station.
An ideal data agreement is a = 0, and b = 1. This presumption is rejected if computed t-value is larger than critical t-value. Level of significance α
= 1 %.
Tested by Computer programme TestMOAR.
Example of excellent agreement between radon data of an organization and medians of radon data of the group of organizations.
RIM 2010Results -
example
Charles University in Prague
Test 2
–
linear regression y = a + bx ( blue) between radon activity concentration cA
reported by the organization (y) and medians of cA
(x) of all organizations in the group. Ideal regression line (a = 0, b = 1)
is marked red.
c
Aof
the organization [kBq/m3]
Median of cA
of all organizations in the group [kBq/m3]
RIM 2010Results -
example
Test No. 2: Linear regression y = a + bx
of radon activity concentration reported by an organization (y) at a single station and median (x) of radon activity concentration of the group of organizations at the same station.
An ideal data agreement is a = 0, and b = 1. This presumption is rejected if computed t-value is larger than critical t-value. Level of significance α
= 1 %.
Tested by Computer programme TestMOAR.
Example of poor
agreement between radon data of an organization and medians of radon data of the group of organizations.
Charles University in Prague
Test No. 3: Comparison of average (AM) radon activity concentration in soil gas at radon reference sites
Normed
radon data R1/R2Criterion R1/R2 ideal value 1.0, acceptable range
(0.7; 1.3)Criterion R1/R2 is applicable for each single reference site
Tested by Computer programme TestMOAR
Reference site
Cetyne Bohostice Buk
Organization Criterion R1/R2 Average R1/R2
A02 1,135 1,075 1,015 1,075
A03 1,108 1,041 1,275 1,141
A04 1,055 1,021 1,094 1,057
A05 0,795 0,725 0,722 0,747
A06 1,230 0,990 1,110
A07 0,834 0,688 0,662 0,728
A08 1,162 1,023 1,410 1,198
A09 1,094 0,872 1,072 1,013
A10 0,960 0,990 1,041 0,997
A11 0,986 1,021 1,004
A12 1,026 0,970 1,012 1,003
A13 1,482 1,360 1,421
RIM 2010Results -
example
Charles University in Prague
Thank you